Java Support via coc.nvim

[tbo]

The Readme mentions, that java support could be gained by integrating something like ycmd. I would propose using coc.nvim for this instead. It has much better language support and even offers bundled language servers. The java extension for coc should already contain a working DAP Server. It is part of eclipse.jdt.ls.

[puremourning]

As a core maintainer of YCM/ycmd, and author of the LSP integration in ycmd, it just makes more sense for me to use that.

I hadn't seen coc before. It's not obvious what advantage it would have in terms of integrating with jdt.ls over what I could do with YCM, but I will take a look.

TBH, reverse engineering the java debug plugin is proving to be pretty tricky, so java support is probably a way off either ways.

[puremourning]

For the record the DAP server is not part of jdt.ls. It's actually an extension bundle that is contributed in the Microsoft/vscode-java-debug VSCode extension, which ultimately boils down to the Microsoft/java-debug-server.

This then does things with VSCode's commands, and LSP's executeCommand abomination, which I have yet to fully get my head around.

[tbo]

For the record the DAP server is not part of jdt.ls. It's actually an extension bundle that is contributed in the Microsoft/vscode-java-debug VSCode extension, which ultimately boils down to the Microsoft/java-debug-server.

You are right. I should have read the whole thread.

[puremourning]

Well, as it happens I have made it work (sort of) with jdt.ls/java debug server without any hard-dependency on the mechanism used for starting the debug server.

vimspector asks the user what port to connect to and does not itself initiate jdt.ls's startDebugSession command.

In my fork of ycmd I have made it possible to send this command to the jdt.ls within ycmd and voila, java debugging works!

I haven't pushed this yet, but I'm quite pleased how simple it turned out to be.

[tbo]

In my fork of ycmd I have made it possible to send this command to the jdt.ls within ycmd and voila, java debugging works!

Nice! Will ycmd be a hard requirement for this or could it be configured to use another LSP-Provider?

[puremourning]

As it stands, there is no dependency on anything. You just have to tell vimspector the port on which the debug adapter is listening. How to start up the debug adapter int his case is not handled by vimspector. It just happens that it is trivial for me to make a ycm command which starts the debug server and returns the port to use. here's a demo:

[puremourning]

https://github.com/puremourning/vimspector/blob/master/support/test/java/test_project/.vimspector.json

[puremourning]

I would like to improve the workflow for firing up the adapter etc, but for now I would declare this "supported" by 14603ae so closing this issue (for now)

[tbo]

@puremourning How exactly did you start the debug plugin? I had a look at java-debug, but couldn't figure it out.

[puremourning]

As you can see in my demo, i'm using a customised version of YouCompleteMe (actually ycmd) to send a custom command to the jdt.ls server.

Ultimately, the way the debug server is started is:

• something, somewhere starts up a jdt.ls instance with the debug adapter "bundle" passed as an additional initialisation option, and connects to it. In my case, this is my fork of ycmd.
• something provides the capability send a Language Server Protocol 'executeCommand' message to that jdt.ls instance (In my case, this is :YcmCompleter ExectuteCommand <arguments>)
• you execute the LSP command java.execute.workspaceCommand with arguments [ 'vscode.java.startDebugSession' ] (In my case, this is :YcmCompleter ExectuteCommand vscode.java.startDebugSession, as in the above demo)

The result of this is a number (a port) which is the TCP port on which the debug adapter is now listening. This is passed to vimspector by setting adapters.<something>.port to "ask".

So you have to be able to execute this custom command implemented by jdt.ls and forwarded to the debug adapter plugin. Because that's the way it is designed. In VSCode, this is all done by the extensions collaborating within the VScode IDE. Vimspector doesn't have all of that (yet?) so it's all a bit manual.

[puremourning]

Feel free to contact me on gitter if you want more info.